1. Field of the Invention
The present invention relates to a vehicle air conditioner for heating a passenger compartment using both of a heater core and a heat pump cycle. The heat core heats air using exhaust heat generated from the vehicle as a heating source. More particularly, the present invention relates to a control of the vehicle air conditioner, when operation of the heat pump cycle is switched from a defrosting operation to a heating operation.
2. Description of Related Art
In a vehicle air conditioner, air to be blown into a passenger compartment is heated in a heater core using hot water (engine-cooling water) as a heating source. In the vehicle air conditioner, when the temperature of the water flowing into the heater core is low, the temperature of air blown into the passenger compartment is reduced, and a necessary heating capacity cannot be obtained. Accordingly, recently, a heat pump cycle is combined with the heater core for improving the heating capacity. That is, when a necessary heating capacity cannot be obtained only by the heater core, a heating operation is performed by operating an interior heat exchanger of the heat pump cycle as a radiator. When the heating operation is performed in the heat pump cycle, a surface of the exterior heat exchanger is readily frosted. When the heat pump cycle is operated while the surface of the exterior heat exchanger is frosted, heat absorption efficiency of the exterior heat exchanger is reduced. In this case, generally, a defrosting operation of the exterior heat exchanger is performed by operating the exterior heat exchanger as a radiator.
On the other hand, after a predetermined time (e.g., one hour) passes after starting an engine, the temperature of hot water is increased, and the necessary heating capacity can be obtained only by the heater core. Accordingly, the heating operation in the heat pump cycle becomes unnecessary at about a time where the surface of the exterior heat exchanger is frosted, for example. Even in this case, when an outside air temperature is equal to or lower than 0° C., because the frost formed once on the surface of the exterior heat exchanger does not melt, the defrosting operation of the exterior heat exchanger is needed to be performed before the heat pump cycle is operated next.
However, when the defrosting operation of the exterior heat exchanger is performed, condensed water is formed on the surface of the interior heat exchanger due to heat absorption of the interior heat exchanger. Then, when the operation of the heat pump cycle is switched from the defrosting operation to the heating operation in such a case where the temperature of the hot water is again reduced, the condensed water on the interior heat exchanger is evaporated due to heat radiation of the interior heat exchanger. Therefore, a windshield of the vehicle may be fogged.